Method of fabricating and processing cathode ray tubes



Aug. 15, 196 A. M. MORRELL METHOD OF FABRICATING AND PROCESSING CATHODERAY TUBES 2 Sheets-Sheet 1 Filed June 12, 1964 2 I i lli lni INVENTOR415577 M Mama;

Off/6y Aug. 15, 1%? A. M. MORRELL METHOD OF FABRICATING AND PROCESSINGCATHODE RAY TUBES 2 Sheets-Shet 2 Filed June 12, 1964 IN VE N TOR. Awe/wM Mawflz United States Patent 3,335,479 METHOD OF FABRICATING ANDPROCESSING CATHGDE RAY TUBES Albert M. Morrell, Lancaster, Pa., assignorto Radio Corporation of America, a corporation of Delaware Filed June12, 1964, Ser. No. 374,691 7 Claims. (Cl. 29-2513) This inventionrelates to the manufacture of cathode ray tubes and particularly to thefabrication of faceplate panel assemblies therefor and to the processingof faceplate panel assemblies and electrodes mounted therein.

In some types of cathode ray tubes, an electrode of substantially thesame siZe as the phosphor screen of the tube is mounted closely adjacentto the screen. For example, the shadow mask cathode ray tube forproducing images in color includes a multiapertured masking elec trodewhich may be spaced about /2 -inch from a mosaic phosphor screen. Thecommercially available RCA 21FBP22 is such a tube.

The envelopes of tubes, which have an electrode mounted adjacent to thescreen, usually include a shallowbowl like glass faceplate panel sealedto a glass funnel member by a low temperature melting glass (frit) suchas described in US. Patent 2,889,952 issued to S. A. Claypool on June 9,1959. The faceplate panel comprises a curved faceplate portion on whichthe phosphor screen is disposed and a peripheral sidewall portion. Aplurality of studs are sealed into or onto the internal surface of thepanel, usually the side wall of the panel, and the mask electrode isremovably mounted thereon by a plurality of spring support elementswhich are attached to the mask and which have apertured plate portionsthat fit over the studs.

It is an object of this invention to provide a novel method forproviding an improved mounting of the electrode support studs onto afaceplate panel.

Another object of the invention is the provision of an improved heattreatment method of processing parts of a cathode ray tube.

It is also an object of this invention to provide an improved assemblyof a faceplate panel and a shadow mask electrode for a cathode ray tube.

The invention disclosed herein may be practiced in the manufacture of acathode ray tube having a mosaic screen comprising a multiplicity ofelemental phosphor deposits critically positioned relative to theapertures of an apertured electrode which is to be mounted in aparticular faceplate panel. In accordance with one feature of theinvention, the electrode is provided with apertured support springsattached thereto and is positioned within the panel in a desired spatialrelationship therewith. One or more studs, a portion thereof which maybe precoated with a glass frit, are inserted into the apertures of thesup port springs so that the springs urge the studs against the interiorsurface of the panel. The assembly of panel, electrode, and studs isthen subjected to a suitable treatment, such as a heating thereof, tosecure the studs to the panel in locations precisely aligned with theirassociated spring apertures.

In accordance with another feature of the invention, either by thisheating or by a separate heating, the electrode and/or panel are heatstabilized to relieve the stresses therein. Subsequent to the attachmentof the studs and the heat stabilization of the electrode and panel, theelemental phosphor deposits of the mosaic screen are applied to thefaceplate panel.

It is often the present practice in the industry in making shadow maskcathode ray tubes to attach the studs to a faceplate panel by the use ofone jig and to attach the support springs to the mask electrode by theuse of a different but related jig. The resulting tolerance of fit ofthe mask on the studs and the tolerance of the mask-toscreen spacing isaccordingly determined by the additive tolerances of the two jigs. Themethod of the present invention avoids the inaccuracies of such additivetolerances since the mask itself is used as the jig for securing thestuds to the panel, thereby providing a custom fit between the maskelectrode and studs.

The improved accuracy of fit between the mask electrode and the studsobtained by my method is especially advantageous in a four stud supportarrangement such as has been proposed for a shadow mask cathode ray tubehaving a rectangular shaped faceplate and mask electrode.

With the general type of spring-stud arrangement described herein, a3-spring mask can always be fited onto its 3-stud panel even though, dueto manufacturing tolerances, the spring aperture array and the studarray are not identically disposed. This is because the mask can beshifted and rotated slightly until each of the three spring apertures isin alignment with its associated stud. Furthermore, the three springswill be received on the three studs with the mask in only one positionrelative to the panel. That is, a 3-point support arrangement of threesprings on three studs determines a unique position of the mask withrelation to the panel. This is true not only for a 3-stud support systembut also for three of the four supports of a 4-stud support system.Thus, in a 4-stud system, the fourth spring and the fourth stud must bepositioned so that they mate precisely with each other when the mask isin the unique position determined by the other three supports.Manufacturing tolerances of the prior art methods described above do notpermit such precise positioning to be readily obtained.

When the studs are secured to the faceplate panel according to mymethod, both the mask electrode and the panel can be completely heatstabilized with respect to temperatures to which they will be subjectedduring subsequent processing and operation thereof. No such heatstabilization of the mask and panel is provided in accordance withpractices of the prior art.

The advantage of a complete heat stabilization of both the maskelectrode and faceplate panel may be explained as follows. In a wideangle deflection shadow mask cathode ray tube, a dot-like phosphordeposit of about 17 mils (l mil=.001 inch) diameter may be excited by anelectron stream which produces an electron spot of about 12 mils indiameter on the phosphor dot. Even when the electron spot is preciselycentered on the phosphor dot there exists only a 2 /2 mil tolerance forspot-dot register. In practice, the electron spot may not be preciselycentered on the phosphor dot. Thus, the tolerance for spotdot registermay be something less than 2 /2 mils, e.g., 1 mil. In prior art shadowmask cathode ray tubes, the mask electrode and faceplate panel are notcompletely heat-stabilized before deposition of the phosphor screen. Themask and screen then can shift relatively to each other during screenbake-out or during operation of the completed tube because of a heatingand stress-relief effect which occurs then. Since this stress reliefoccurs after the phosphor screen has been deposited, there is a changeof register between the phosphor dot and the electron spot. However, ifthe tube is heat stabilized as disclosed herein, there is little or nostress-relief effect to cause change of registry of phosphor dot andelectron spot, and a product superior in use to the prior art product isattained.

In the drawing:

FIG. 1 is a plan view of a studded cathode ray tube faceplate panel andapertured mask electrode together with a spacing fixture utilized insecuring the studs to the p anel;

FIG. 2 is a sectional view taken along line 22 of FIG. 1;

FIG. 3 is an enlarged elevation view of a portion of the device of FIG.1 taken along line 3-3 thereof; and

FIGS. 4 and 5 are sectional views of one of the mask mounting studs ofFIG. 1 illustrating different process modifications and stages thereofin the securing of the studs to the panel.

With reference to the drawing, a cathode ray tube glass faceplate panelcomprises a generally rectangular faceplate 12 and a side wall 14extending from the periphery of the faceplate. The faceplate 12 ispreferably curved, e.g., with an approximately spherical contour, as isknown in the art. A plurality of electrode mounting studs 16 areattached to the interior surface of the panel side wall 14, preferablyone near the mid-point of each of the two long sides 18 and the twoshort sides 20. As best shown in FIGS. 3, 4, and 5, each stud 16comprises a hollow circular cup-shaped element having a tapered circulartip 22 forming the bottom of the cup.

A shadow mask electrode 24, mounted within the faceplate panel It),includes a frame member 26, a masking member 28, and a plurality ofsupport leaf springs 30. The frame 26 comprises a closed, generallyrectangular rim having an L-shaped cross section. The masking member 28comprises a shallow bowl-like multiapertured sheet of metal mountedacross the frame 26. The mask member 28 has a surface contour whichapproximately matches the surface contour of the faceplate 12, forexample, as described in US. Patent 3,109,116 issued to D. W. Epstein etal., on October 29, 1963. Each of the leaf springs 30 (see particularlyFIG. 1) has one of its ends attached to the side of the frame-maskassembly 26-28 and an opposite end off-set radially outwardly from theside of the frame-mask assembly and provided with an aperture 32. Theaperture 32 is preferably of a generally triangular shape (FIG. 3), andthe springs are so located that the apertures 32 receive the roundtapered tips 22 of the studs 16 in a three point contact (or three smallarea contacts) therewith.

Before attaching the studs 16 to the panel side wall 14, the studs arepreferably prepared by providing them with a precoating of a bondingagent such as a devitrifiable glass frit. In accordance with a preferredpractice, the cup shaped stud 16 is filled with a slurry of glass fritsuspended in a binder such as nitrocellulose. The stud 16 and fritslurry are then heated to a temperature sufficient to volatize thebinder and soften the frit to thereby cause it to glaze, or adhere to,the inner wall of the stud 16. As shown in FIG. 4, the frit 34 is ofsuch a quantity that when glazed to the stud 16 it substantially fillsthe large cup portion of the stud 16 and protrudes very slightly beyondthe open end of the stud in a shallow mound 36.

The shadow mask electrode 24, including the frame 26, the masking member28, and the support springs 30 are provided as a unit and positioned ontop of a spacer device 38 within a studless faceplate panel 10. Suchmethod of positioning provides an extremely accurate strain-freespacing. The panel may be oriented open-end-up as shown in FIG. 2 sothat gravity urges the mask electrode 24 against the spacer 38 and thespacer against the panel 10. The spacer device 38 includes a T-shapedmember whose three arms 39, 40, 41 extend to points adjacent to thepanel side wall 14. Spacer pads 42 are provided near the ends of thearms 39, 40, 41 and extend therefrom to contact the faceplate 12.Mask-support brackets 44 are attached to the ends of the spacer arms 39,40, 41 for receiving the mask electrode 24 in desired spacedrelationship with the faceplate 12.

If desired the assembly of the panel 10, spacer 38, and mask electrode24 may be inverted with the mask electrode being supported and the panelresting thereupon.

With the mask electrode 24 in position within the faceplate panel 10,the frit coated studs 16 (as shown in FIG. 4) are inserted between thesupport springs 30 and the panel side wall 14, with the tapered tips 22received within the apertures 32 of the support springs and with thefrit mounds 36 in contact with the interior surface of the panel sidewall 14. In such an arrangement, the frit coated studs 16 are urged bythe support springs 30 against the panel side wall 14.

The entire assembly of faceplate panel 10, mask electrode 24, and studs16 is then heated to resoften the frit coating on the studs 16. Theparticular time and temperature schedule to produce a softening of thefrit is dependent upon the particular type of frit used. After the frithas become softened and the studs 16 pressed into place against thepanel side wall 14, the frit is allowed to solidify and permanentlysecure the studs to the panel side Wall. In the case of a devitrifiablefrit such as that marketed by the Corning Glass Company and identifiedby them as 7572, the solidification of the frit may occur at an elevatedtemperature. Such a devitrifiable frit is preferred because of itssubsequent resistance to high temperature treatment during laterprocessing of the cathode ray tube. In the case of a non-devitrifiablefrit, the assembly of faceplate panel, mask electrode, and studs iscooled to produce a solidification of the frit.

The above-described method of attaching the studs 16 to the panel 10 maybe used to secure either all of the studs or any partial number of them,to a faceplate panel. For example, in a 4-stud panel, three of the studsmay be sealed into the panel by a prior art method, and the maskelectrode may be provided with its four support springs. Then the maskmay be supported within the panel with three of the support springsmounted on the three existing studs, and the fourth stud may then befrit sealed to the panel as hereinbefore described. In such afabrication procedure, the spacing device 38 may be dispensed with sincethe mask can be supported in place within the panel on the threeexisting studs during sealing-in of the fourth stud.

When one or more studs are frit sealed to the panel as described above,both the mask 24 and the panel 10 can be conveniently heatedsimultaneously to a heat-stabilizing temperature as high as or higherthan that to which they will be heated in subsequent processing oroperation of the tube. This heat-stabilizing heating causes stresses inthe mask and panel to be relieved and results in a relaxing andattendant minute reshaping of the mask and panel. Subsequent heatings ofthe mask and panel cause no significant additional stress relief and noreshaping of the mask and panel, as long as the subsequent heating doesnot raise the mask or panel to a temperature higher than the previousheat-stabilizing temperature. The mask and panel may be considered to becompletely heatstabilized for subsequent normal processing andoperation.

As an alternative to heat stabilizing the mask and panel together, theymay be heat stabilized by separate hetaings. For example, it may bedesirable and/ or convenient for the glass panel to be heat stabilizedby the manufacturer of the panel. In any event such a separateheat-stabilizing treatment of the panel should be at a temperature atleast as high as the highest temperature to which it will besubsequently subjected by the tube manufacturer.

In attaching the studs to the panel, it may not be desirable to use atemperature equal to or greater than all subsequently encounteredtemperatures. In such cases, a separate heating of the mask and panelshould be employed before application of the phosphor screen so as toraise the mask and panel to a suitable heat-stabilizing temperature asdescribed above. The lack of accurate spotdot register which may resultfrom heating of the mask and panel in later use or processing is thusprevented.

If desired, the frit 34 may be provided as a pellet 46 as shown in FIG.5. The pellet 46 may be inserted into a cup-shaped stud 16 a the timethe stud is inserted in the apertures 32 a support spring 30. The firstpellets are then held in place within the studs by the spring pressureurging them against the panel side wall 14. The bonding,

or glazing, of the frit thus occurs simultaneously to both the stud 16and the side wall 14 when the assembly is heated. Alternatively, thefrit pellet 46 may be heated in its stud prior to assembly of the studwithin the spring aperture to preglaze the frit of the pellet to thestud as shown in FIG. 4.

As another alternative, the frit may be applied to the panel sidewall14. The studs, with or without a coating of frit, are then pressedagainst the fritted areas of the side-wall. In such case it may bepreferred to use a solid stud or a stud having a closed, flush endadjacent to the side wall 14. In this alternative, the frit may beprovided in the form of an adhesive-backed tape comprising fritsuspended in a solidified organic binder such as nitrocellulose.Furthermore, whether the frit is provided as a tape or otherwise, it maybe applied to the panel side wall 14 over an area considerably largerthan the stud. Such a large-area application of frit may serve toadvantageously reduce stress concentration at the seal between the studand panel.

In accordance with one practice of the invention, the faceplate panelmay comprise a glass marketed by the Corning Glass Company andidentified by them as 9019. The studs 16 may comprise industry standardN71 stainless steel, an alloy of principally nickel and iron, and thefrit may comprise the devitrifiable 7572 frit referred to above. Theprecoating of the studs \16 with the frit may be performed at 340400 C.and the subsequent softening and devitrifying of the frit coating on thestud performed at a temperature of 445 C.

This invention has been disclosed by way of example, as embodying aparticular design of multiapertured shadow mask electrode including aparticular support spring design and a particular design of maskmounting studs. However, other designs of these elements may be used.

Furthermore, means other than a glass frit as herein disclosed may beused to bond the studs to the faceplace panel. For example, otherbonding materials such as Sauereisen cement may be used. Alternatively,a selected area of the faceplate panel may be metalized and the studssoldered thereto.

What is claimed is:

1. In the manufacture of cathode ray tubes of the type comprising afaceplate panel having a plurality of studs attached thereto byheat-sealing which are received within the apertures of a plurality ofspring supports attached to a mask electrode, the method of attachingsaid studs to said faceplate panel, said method comprising the steps of:

(a) disposing said mask and said panel in a desired spatial relationshipwith each other,

(b) positioning said studs in the apertures of said spring supports sothat said studs are pressed against said panel by the spring action ofsaid spring support elements, and

(c) then heating the assembly of said panel, mask electrode, and studsto as high a temperature above the heat-sealing temperature as thehighest temperature to which said assembly is to be subjected duringsubsequent processing and operation to secure said studs to said panelin locations corresponding precisely to the locations of said springsupports and to heat stabilize said mask electrode and said panel sothat stresses therein are substantially relieved when the said electrodeis subsequently supported on said studs and said tube is operated.

2. In the manufacture of a cathode ray tube of the type having anelectrode to which are attached a plurality of apertured supportelements which are received on respectively different mounting studssecured by heat-sealing to the internal surface of the side wall of ashallow bowl-shaped faceplate panel, the method of mounting asidelectrode in said panel comprising the steps of:

(a) coating a portion of one of said studs with glass frit,

(b) inserting said stud in the aperture of one of said support elements,

(0) assembling said electrode and stud within said panel with saidelectrode in a given spatial relationship with said panel and with thefrit on said stud in contact with the side wall of said panel,

(d) then heating the assembly of said electrode and panel to as high atemperature above the heat-sealing temperature as the highesttemperature to which said assembly is to be subjected during subsequentprocessing and operation to heat stabilize said electrode and said paneland to soften said frit, and

(e) hardening said frit to secure said stud to said panel.

3. In the manufacture of a cathode ray tube of the type comprising amultiapertured sheet metal mask electrode which includes a plurality ofapertured support springs at the periphery thereof, a shallowbowl-shaped faceplate panel including a face-plate portion and aperipheral side Wall portion, and a plurality of cup-shaped mountingstuds secured to the internal surface of said side wall and received inthe apertures of said support springs, the method of mounting said maskin said panel which method comprises the steps of:

(a) depositing quantities of devitrifiable glass frit in said cup-shapedstuds and glazing said frit thereto so that said frit protrudes slightlyfrom the open ends of said studs,

(b) inserting said studs in the apertures of said support springs,disposing said electrode within said panel and urging said electrodewith said studs in the support springs thereof toward said panel with aspacer device disposed between said electrode and the internal surfaceof said faceplate portion, with the frit on said studs being pressedinto contact with said side wall by said support springs,

(d) then heating the assembly of said electrode, studs, and panel to ashigh a temperature as the highest temperature to which said assembly isto be subjected during subsequent processing and operation to heatstabilize said mask and said panel and soften said frit, and

(e) devitrifying said frit to secure said studs to said panel atlocations corresponding to the locations of said support springs.

4. In the manufacture of a cathode ray tube of the type having amultiapertured shadow mask electrode to which are attached a pluralityof apertured support springs received on respectively different mountingstuds secured by heat-sealing to the internal surface of the side wallof a shallow bowl-shaped faceplate panel on which is provided a mosaicscreen including a multiplicity of dot-like phosphor deposits criticallypositioned relative to the apertures of said mask, the method ofmounting said mask in said panel and simultaneously heat stabilizingsaid mask and panel comprising the steps of:

(a; coating a portion of each of said studs with glass rit,

(b) inserting said studs in the elements,

(c) assembling said electrode and studs within said panel with saidelectrode in a given spatial relationship with said panel and with thefrit on said studs in contact with the side wall of said panel,

((1) then heating the assembly of said electrode and panel to atemperature above the heat-sealing temperature as high as the highesttemperature to which said mask and panel will be subjected duringsubsequent processing and operation thereof, whereby to heat-stabilizesaid mask and panel assembly and to soften said frit,

(e) hardening said frit to secure said studs to said panel, and then (f)applying the dot-like phosphor deposits of said mosaic screen onto theheat-stabilized faceplate panel.

apertures of said support 5. In the manufacture of cathode ray tubes ofthe type comprising a faceplate panel and a multi-apertured maskelectrode mounted on said panel in a predetermined spaced relationthereto, said panel including a mosaic phosphor screen comprising amultiplicity of elemental phosphor deposits critically positionedrelative to the apertures of said mask electrode; the method comprisingthe steps of:

(a) mounting said mask electrode on Said panel in said predeterminedrelation;

(b) then heating the assembly of said panel and mask electrode to ashigh a temperature as the highest temperature to which said panel andmask electrode will be subjected during subsequent processing andoperation thereof to relieve the stresses therein and thus heatstabilize said assembly, and

(c) then depositing the elemental phosphor deposits of said mosaicscreen on said panel.

6. The method of claim 5, wherein said mask electrode is removablymounted on said panel in step (a) by 8 means of a plurality of springsupports secured to said mask electrode and having apertures engaging alike plurality of studs secured to said panel.

7. The method of claim 5, wherein said assembly is heated to atemperature of at least 445 C., in step (b).

References Cited UNITED STATES PATENTS 2,546,828 3/1951 Levy 29-2513 X2,727,172 12/1955 Mark 313-64 X 2,846,608 8/1958 Shrader 313-852,871,087 1/1959 Knochel 29-25.13 X 2,878,623 3/ 1959 Vincent.

2,922,063 1/1960 Haas 313-85 2,928,967 3/1960 Pfaender 313-64 3,187,4046/1965 Fiore 29-2515 WILLIAM I. BROOKS, Primaly Examiner.

JOHN F. CAMPBELL, Examiner.

1. IN THE MANUFACTURE OF CATHODE RAY TUBES OF THE TYPE COMPRISING AFACEPLATE PANEL HAVING A PLURALITY OF STUDS ATTACHED THERETO BYHEAT-SEALING WHICH ARE RECEIVED WITHIN THE APERTURES OF A PLURALITY OFSPRING SUPPORTS ATTACHED TO A MASK ELECTRODE, THE METHOD OF ATTACHINGSAID STUDS TO SAID FACEPLATE PANEL, SAID METHOD COMPRISING THE STEPS OF:(A) DISPOSING SAID MASK AND SAID PANEL IN A DESIRED SPATIAL RELATIONSHIPWITH EACH OTHER, (B) POSITIONING SAID STUDS IN THE APERTURES OF SAIDSPRING SUPPORTS SO THAT SAID STUDS ARE PRESSED AGAINST SAID PANEL BY THESPRING ACTION OF SAID SPRING SUPPORT ELEMENTS, AND (C) THEN HEATING THEASSEMBLY OF SAID PANEL, MASK ELECTRODE, AND STUDS TO AS HIGH ATEMPERATURE ABOVE THE HEAT-SEALING TEMPERATURE AS THE HIGHESTTEMPERATURE TO WHICH SAID ASSEMBLY IS TO BE SUBJECTED DURING SUBSEQUENTPROCESSING AND OPERATION TO SECURE SAID STUDS